The railroad's on-time performance cratered over the summer, with the number of trains on time overall dropping below 90 percent for the first time in at least five years, and morning rush hour trains on the Hudson Line dropping below 80 percent in August.

Officials blame a massive years-old backlog of maintenance that is catching up with a railroad that has set four consecutive annual ridership records.

On top of that, a rush to install the safety system positive train control technology is leading to equipment shortages, and fewer seats.

Metro-North communicates information about delays and cancellations via its Twitter account, text message and email. But if you're a commuting newbie, or even a seasoned rail rider who prefers to simply sit back and enjoy the ride, sometimes the terminology could use some clearing up.

So, The Journal News/lohud looked at some of the most frequently used terms in Metro-North communications to come up with a list to help demystify what's going on in your commute.

Call it the Metro-North Dictionary. Or the ABC's of the MTA.

A person needing medical assistance

A person experiencing a medical emergency that requires removal from the train. The exact problem could be anything from a heart attack or a seizure to someone falling down or someone who is intoxicated and passed out.

AM Peak

The AM Peak — or morning peak — are trains scheduled to get into Grand Central Terminal or Harlem-125th Street between 5 and 10 a.m. on weekday mornings. Fares are higher during these hours.

AM Reverse Peak

The AM reverse peak are trains that leave Grand Central Terminal or Harlem-125th Street between 5:30 a.m. and 9 a.m. on weekday mornings. They are primarily used by reverse commuters who live in New York City and work in the Lower Hudson Valley or Connecticut. Fares are higher during these hours.

Catenary wires

The wires over Metro-North New Haven Line tracks that supply trains with electricity with which to run. Trains have pantograph arms that stick up off the top to access the power.

The system is left over from when the New Haven Line was run by the New York, New Haven and Hartford Railroad. Only the New Haven Line north of Mount Vernon East uses this system. All other trains are either powered by a locomotive or a third rail.

Circuit issues

When the electrical current traveling through the rails is compromised.

Metro-North runs a tiny electrical current through the rails, separate from the third rail, as part of its signaling system. The current is organized into "signal blocks" that cover 500 feet to 3,000 feet of rail and help detect trains, as well as breaks or flaws in the track.

When the current stops, the signal systems go red, stopping trains from traveling over tracks that could be dangerous.

"Larchmont Larry" got his nickname when he first began his Metro-North career as a ticket agent in Larchmont.(Photo: Colleen Ferguson)

Conductor

Generally responsible for taking tickets on the train.

Consist compliance

The percentage of trains where the number of seats provided was greater than or equal to the required number of seats per loading standards.

Deadhead

A train not in revenue service — meaning the train might be moving on Metro-North’s tracks, but it’s not picking any passengers up.

Disabled train

A train that cannot proceed.

Metro-North uses this term when they do not have time to fully diagnose the problem.

Engineer

The person responsible for driving the train.

Like drivers, engineers have signals telling them when they can proceed, speed limits letting them know the safest speed to travel and a dashboard complete with warning lights letting them know if anything is wrong with the train.

Late connection

When a train that offers a connection to another train is late arriving to a station, and thus misses its connection.

Branch line trains are scheduled to make connections with main line trains for seamless travel, as are express and local trains for passengers using intermediate stops. If one of the trains is late, passengers cannot make the connection.

Locomotive

The piece of rolling stock that powers the train. In the Metro-North system, diesel-powered locomotives are used on portions of the system that are not electrified, like the Hudson Line north of Croton-Harmon and the Harlem Line north of Southeast.

More than 4,700 people get on Hudson Line trains each day at Croton-Harmon station, making it the third busiest Metro-North station in Westchester, Rockland and Putnam counties. Ricky Flores/The Journal News

With more than 3,300 commuters getting on the train each weekday, Bronxville station is the sixth busiest in the Lower Hudson Valley and 14th largest in the Metro-North system. Seth Harrison/The Journal News

Hartsdale station is where more than 3,100 commuters get on the train each morning, making it the ninth busest Metro-North station in Westchester, Rockland and Putnam counties. Dave Gershman via Twitter

Interested in this topic? You may also want to view these photo galleries:

Mean distance between failure

The average number of miles a rail car or locomotive travels in revenue service before breaking down and causing a delay. The higher the mean distance between failures, the more reliable the equipment and the service.

Mechanical difficulties

A problem with the train itself.

Trains have many moving parts, ranging from compressors to air hoses to brake valves to electrical transformers and more. Mechanical difficulties are when something with those systems go wrong and needs fixing.

Off-Peak

If a train’s arrival or departure from Grand Central Terminal or Harlem-125th Street does not fall within AM, AM reverse or PM peak hours — basically, if it’s not during the morning or evening rushes — it is an off-peak train. All weekend trains are considered off peak. Fares are lower for off-peak trains.

On-Time

A train is considered on time if it arrives at its scheduled destination within 6 minutes of its scheduled arrival. This is a national industry standard, according to the railroad.

Pantograph

The arm that sticks off the top of New Haven Line trains to access electrical power via catenary wires.

Police activity

A police response that requires Metro-North to halt train traffic.

Police activity can encompass any number of issues, from disruptive passengers on trains to chases where a suspect runs onto the tracks to someone throwing themselves in front of a train. The term covers activity from both local police and MTA Police.

Metro-North Railroad workers replace track along the Harlem Line just north of the Brewster Train Station April 21, 2018.(Photo: Frank Becerra Jr./The Journal News)

Positive train control

Positive train control is safety technology that can slow a train down or stop it to prevent derailments and collisions.

The technology incorporates devices on tracks and trains and along railroad rights of way, plus radio spectrum and back end computer systems to do so.

Congress mandated the technology be implemented on all railroads in 2008, after a head-on collision in Los Angeles. Railroads were given a three-year extension until Dec. 31, 2018, in 2015, with the further possibility of another two-year extension, should certain installation thresholds be met. Metro-North intends to get the two-year extension.

The National Transportation Safety Board said positive train control would have prevented the 2013 Spuyten Duyvil derailment.

Power issues

Problems with the third rail or catenary wire systems that power most of the railroad's trains.

The problem can be either with Metro-North infrastructure or the providers which electrify those systems — Con Edison in New York and Eversource Energy and United Illuminating in Connecticut.

Residual delays

Delays that continue after the issue causing a delayed train has been cleared up.

For example, Train A might be delayed due to a downed tree branch. Once the railroad has cleared that branch out of the way, Train B, traveling behind Train A, might be slightly late as well, given that all train traffic behind Train A had to slow down.

Rolling stock

All train cars and locomotives employed by Metro-North to transport passengers.

Signal issues

A problem with the signaling system that tells engineers if it is safe to go or if they must stop.

Single tracking

Trains in both directions will only be operating on one set of track. This is done when work is being carried out on one set of tracks and is usually only done for a portion of the line.

Slip-slide conditions

A slippery condition created when crushed leaves leave a slimy substance on train tracks, which get even more slippery after it rains. This gelatinous slime can cause a train's wheels to slip or slide on the tracks when a train tries to speed up or slow down. Braking during slip-slide conditions can create flat spots on a train's wheels, which must then be repaired.

Speed restrictions

Like local roads and highways, tracks have speed limits that engineers are supposed to abide by, too. Metro-North will put speed restrictions in place if there is work being performed on the tracks or wayside areas or in the case of extreme heat or cold.

Switch issues

Issues with the rail infrastructure that moves trains from one set of tracks to another.

Switches are parts of the railroad that physically move to reroute trains. If trains cannot switch between sets of tracks, trains can back up.

Third rail

The power system on Harlem Line trains south of Southeast, Hudson Line trains south of Croton-Harmon and New Haven Line trains south of Mount Vernon East use for power. The third rail runs parallel to tracks, and is accessed via a “shoe” that makes contact with the underside of the heavily electrified rail. The top is covered.

The system was implemented more than 100 years ago, when the state passed a law banning steam engines from Manhattan after a deadly crash involving trains from White Plains and Norwalk, Connecticut. Metro-North’s predecessor railroads chose various means of providing electric power and New York Central, which ran the present-day Harlem and Hudson lines, chose a third rail.

Tie

The wooden part of the tracks that run perpendicular to the rails.

On Metro-North, the ties are either wooden or concrete.

Track geometry

The characteristics of the track as far as position, curvature, alignment and smoothness. Railroads worldwide use track geometry cars to monitor track geometry and to find out which stretches of track might need work.

Unauthorized person on the tracks

When anyone, who doesn't have prior clearance from Metro-North, makes their way onto the tracks.

Metro-North clears various people, primarily employees, police and contractors to be on the tracks, mainly to perform track work. When someone without clearance and the proper safety training goes on the tracks, it creates a potentially dangerous situation for both the individual and the railroad.

Undercutting

Work that lowers track height to a more appropriate level.

As part of track maintenance, Metro-North often employs a machine to lift track, tamp down the stone that forms the track bed – also known as the ballast – and secure the tracks in place. But this process raises track height, which can cause issues when trains must pass under a bridge or, in the case of New Haven Line trains, access power from fixed wires over the train.